Method and device for selecting long term evolution lte network

ABSTRACT

A method and device for selecting an LTE network, relating to the technical field of communications, are disclosed in the present application are, which makes that a UE can returns to an LTE PLMN registered when CSFB is initiated after the CSFB service, thereby ensuring the continuity of PS service, avoiding an unnecessary inter-PLMN network switch and promoting the user experience. The method provided in the present application mainly comprises: performing, by a UE, a combined registration in the LTE PLMN; initiates, by the UE, a CSFB service to fall back to a 2G/3G network, and receiving an equivalent PLMN list in the 2G/3G network; adding, by the UE, identity information of the LTE PLMN to the equivalent PLMN list; performing, by the UE, a PLMN selection according to the equivalent PLMN list when the CSFB service ends.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/CN2013/070283, filed on Jan. 9, 2013, which is hereby incorporatedby reference in its entirety.

TECHNICAL FIELD

The present application relates to the technical field ofcommunications, and particularly relates to a method and device forselecting a Long Term Evolution (LTE) network when a Circuit DomainFallback (CSFB) service ends.

BACKGROUND

A Circuit Domain (CS) network is a wireless network for providingcircuit domain services such as a voice call and the like, and thecoverage of a 2nd Generation/3rd Generation (2G/3G) network such as GSM,WCDMA and the like is very universal. Meanwhile, with a development of anetwork technology, a packet domain (PS) network, such as a Long TermEvolution (LTE) network, which specializes in providing a data service,is being deployed in a large scale. Therefore, the CS domain network andthe PS domain network co-exist in present communication networks, and anoperator may provide a circuit domain service for a user by using a2G/3G network and provide a data service for a user by using an LTEnetwork.

Based on this network coverage mode, the 3rd Generation PartnershipProject (3GPP) organization proposes a “circuit switched fallback”(CSFB) technology, so that a user equipment (UE) registered to the LTEnetwork returns to a CS domain of a 2G/3G network to complete theservice processing when a CS voice service is required to be processed.In a situation that the CS voice call is finished, the present protocolfurther defines a CSFB return mechanism to ensure that a UE may returnto the PS domain network to perform a PS service after a CS voice callis finished, which specifically includes: a Mobile Switching Centre(MSC)/Visitors Location Register (VLR) releases a connection establishedby a CS voice call and indicates a base station that the currentconnection is established due to a CSFB; and the base station indicatesLTE frequency band information for a UE to reselect an LTE network backwhen the base station releases the connection, so that when a suitablecell on the LTE frequency band corresponding to the LTE frequency bandinformation is redirected, the UE randomly selects an available LTEPublic Land Mobile Network (PLMN) in broadcast information of thesuitable cell.

In the process of realizing the aforementioned returning to an LTEnetwork, the inventor discovers that there exists at least the followingproblems in the prior art: since a UE is probably in LTE networkcoverage of several different PLMNs when a CS domain voice service ends,for example, both an LTE PLMN registered by the UE when a CSFB isinitiated and an LTE network of a PLMN of the current CS service areavailable for the UE, and typically, if the UE enters a shared LTE cellwhen the CS voice service is finished, the UE may acquire severalavailable LTE PLMNs in the LTE cell. Under the scenario that several LTEPLMNs are available, it can not be ensured for the UE, in the prior art,to select a previous LTE PLMN registered when the CSFB service wasinitiated, and if the UE reselects an LTE network of other PLMNs, thedata service suspended in the LTE PLMN registered before the CSFBservice is triggered can not be recovered, which causing a terminationof the on-going data service, and at the same time, causing anunnecessary inter-PLMN switch, thereby affecting service experience of auser.

SUMMARY

A method and device for selecting an LTE network are provided inembodiments of the present application, which makes that a UE can returnto an LTE PLMN registered when a CSFB is initiated after the CSFBservice ends, thereby ensuring the continuity of a PS service, avoidingan unnecessary inter-PLMN switch, and improving service efficiency andpromoting user experience.

To achieve the aforementioned objectives, the following technicalsolutions are adopted in the embodiments of the present application.

In the first aspect of the present application, a method for selectingan LTE network is provided, comprising: performing, by a UE, a combinedregistration in an LTE PLMN; initiating, by the UE, a CSFB service tofall back to a 2G/3G network; receiving, by the UE, an equivalent PLMNlist in the 2G/3G network; adding, by the UE, identity information ofthe LTE PLMN to the equivalent PLMN list; and performing, by the UE, aPLMN selection according to the equivalent PLMN list when the CSFBservice ends.

In combination with the first aspect of the present application, in aprobable way of implementation, the performing a PLMN selectionaccording to the equivalent PLMN list comprises: selecting the LTE PLMNin priority according to the equivalent PLMN list.

In combination with the first aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, the selecting the LTE PLMN in priority comprises:selecting, according to the equivalent PLMN list, a cell on a frequencyband corresponding to LTE frequency band information; and selecting theLTE PLMN in priority from available PLMNs for the cell; wherein, the LTEfrequency band information is information of an LTE frequency bandselected by the UE when the UE initiates a combined registration to theLTE PLMN.

In combination with the first aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, the selecting the LTE PLMN in priority comprises:selecting, according to the equivalent PLMN list, a cell on a frequencyband corresponding to LTE frequency band information; and selecting theLTE PLMN in priority from available PLMNs for the cell; wherein, the LTEfrequency band information is received from the 2G/3G network by the UE.

In the second aspect of the present application, a method for selectingan LTE network is provided, comprising: performing, by a UE, a combinedregistration in an LTE PLMN; performing, by the UE, a PLMN selection ona frequency band corresponding to LTE frequency band information when aCSFB service ends, wherein, the LTE frequency band information isinformation of an LTE frequency band selected by the UE when the UEinitiates a combined registration to the LTE PLMN.

In combination with the second aspect of the present application, in aprobable way of implementation, the performing, by the UE, a PLMNselection on the frequency band corresponding to the LTE frequency bandinformation, comprises: selecting, by the UE, a cell on the frequencyband corresponding to the LTE frequency band information; and selectingthe LTE PLMN in priority from available PLMNs for the cell.

In combination with the second aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, the method further comprises: storing the LTEfrequency band information when the UE initiates the CSFB service andfalls back to a circuit domain.

In the third aspect of the present application, a method for selectingan LTE network is provided, comprising: receiving, by a 2G/3G basestation, a connection release message sent by a serving MSC/VLR,wherein, the connection release message comprises identity informationof an LTE PLMN registered when a UE initiates a CSFB service, and the2G/3G base station is a base station which provides a service for theCSFB service; selecting, by the 2G/3G base station, target frequencyband information according to the identity information of the LTE PLMN;and sending the target frequency band information to the UE, wherein,the target frequency band information is used for indicating the UE toselect a cell for residing on a frequency band corresponding to thetarget frequency band information.

In combination with the third aspect of the present application, in aprobable way of implementation, the sending the target frequency bandinformation to the UE comprises: sending priority information to the UE,wherein, the priority information comprises the frequency bandinformation.

In the fourth aspect of the present application, a method for selectingan LTE network is provided, comprising: receiving, by an LTE basestation, a connection establishment request message sent by the UE whena CSFB service ends, wherein, the connection establishment requestmessage comprises an identity of the UE; and selecting, by the LTE basestation, in accordance with the identity of the UE and identityinformation of an LTE PLMN registered when the UE initiates the CSFBservice, the LTE PLMN corresponding to the identity information of theLTE PLMN.

In combination with the fourth aspect of the present application, in aprobable way of implementation, the method further comprises: receivingand storing, by the LTE base station, the identity of the UE and theidentity information of the LTE PLMN, which are sent by a 2G/3G basestation, wherein, the 2G/3G base station is a base station whichprovides service for the CSFB service.

In combination with the fourth aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, before receiving, by the LTE base station, theidentity of the UE and the identity information of the LTE PLMN, whichare sent by the 2G/3G base station, the method further comprises:receiving, by the 2G/3G base station, a connection release message sentby a serving MSC/VLR, wherein, the connection release message comprisesthe identity of the UE and the identity information of the LTE PLMN;sending, by the 2G/3G base station, the identity of the UE and theidentity information of the LTE PLMN to the LTE base station.

In combination with the fourth aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, if the serving MSC/VLR is a registered MSC/VLR of theUE, the identity of the UE and the identity information of the LTE PLMNare acquired, by the serving MSC/VLR, from registration information ofthe UE; or, if the serving MSC/VLR is not a registered MSC/VLR of theUE, the identity of the UE and the identity information of the LTE PLMNare acquired, by the serving MSC/VLR, from the registered MSC/VLR of theUE.

In combination with the fourth aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, the LTE base station is a base station which providesan access service when the UE initiates the CSFB service, and the methodfurther comprises: storing, by the LTE base station, the identity of theUE and the identity information of the LTE PLMN when the UE initiatesthe CSFB service in the LTE PLMN.

In combination with the fourth aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, the method further comprises: deleting, by the LTEbase station, the stored identity of the UE and the identity informationof the LTE PLMN.

In the fifth aspect of the present application, a UE is provided,comprising: a receiver, configured to receive an equivalent PLMN listfrom a 2G/3G network when the UE performs a combined registration in anLTE PLMN, initiates a CSFB service and falls back to the 2G/3G network;and a processor, configured to add identity information of the LTE PLMNto the equivalent PLMN list received by the receiver, and perform,according to the equivalent PLMN list, a PLMN selection when the CSFBservice ends.

In combination with the fifth aspect of the present application, in aprobable way of implementation, the processor is configured to: selectthe LTE PLMN in priority according to the equivalent PLMN list.

In combination with the fifth aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, the processor is configured to: select, according tothe equivalent PLMN list, a cell on a frequency band corresponding toLTE frequency band information; and select the LTE PLMN in priority fromavailable PLMNs for the cell; wherein, the LTE frequency bandinformation is information of an LTE frequency band selected by the UEwhen the UE initiates a combined registration to the LTE PLMN.

In combination with the fifth aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, the processor is configured to: select, according tothe equivalent PLMN list, a cell on a frequency band corresponding toLTE frequency band information; and select the LTE PLMN in priority fromavailable PLMNs for the cell; wherein, the LTE frequency bandinformation is received, by the UE, from the 2G/3G network.

In the sixth aspect of the present application, a UE is provided,comprising: a transceiver, configured to interact with a network deviceto perform a combined registration in an LTE PLMN; and a processor,configured to perform a PLMN selection on a frequency band correspondingto LTE frequency band information when a CSFB service ends, wherein, theLTE frequency band information is information of an LTE frequency bandselected by the UE when the UE initiates a combined registration to theLTE PLMN.

In combination with the sixth aspect of the present application, in aprobable way of implementation, the processor is configured to: select acell on the frequency band corresponding to the LTE frequency bandinformation, and select the LTE PLMN in priority from available PLMNsfor the cell.

In combination with the sixth aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, the UE further comprising: a storage, configured tostore the LTE frequency band information when the transceiver initiatesthe CSFB service to fall back to a circuit domain, wherein the processoris also configured to acquire the LTE frequency band information fromthe storage when the CSFB service ends.

In the seventh aspect of the present application, a 2G/3G base stationis provided, configured to provide service for a CSFB service,comprising: a receiver, configured to receive a connection releasemessage sent by a serving MSC/VLR, wherein, the connection releasemessage comprises identity information of an LTE PLMN registered when aUE initiates a CSFB service; a processor, configured to select,according to the identity information of the LTE PLMN which is receivedby the receiver, target frequency band information, wherein, the targetfrequency band information is used for indicating the UE to select acell for residing on a frequency band corresponding to the targetfrequency band information; a transmitter, configured to send the targetfrequency band information selected by the processor to the UE.

In combination with the seventh aspect of the present application, in aprobable way of implementation, the transmitter is configured to: sendpriority information to the UE, wherein, the priority informationcomprises the frequency band information.

In the eighth aspect of the present application, an LTE base station,comprising: a receiver, configured to receive a connection establishmentrequest message sent by a UE when a CSFB service ends, wherein, theconnection establishment request message comprises an identity of theUE; and a processor, configured to select, according to the identity ofthe UE and identity information of the LTE PLMN registered when the UEinitiates the CSFB service, the LTE PLMN corresponding to the identityinformation of the LTE PLMN.

In combination with the eighth aspect of the present application, in aprobable way of implementation, the LTE base station further comprises:a storage, wherein the receiver is further configured to receive theidentity of the UE and the identity information of the LTE PLMN, whichare sent by a 2G/3G base station, wherein, the 2G/3G base station is abase station which provides service for the CSFB service; and thestorage is configured to store the identity of the UE and the identityinformation of the LTE PLMN, which are sent by the 2G/3G base stationand received by the receiver.

In combination with the eighth aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, the LTE base station further comprises: atransmitter, wherein the receiver is further configured to receive aconnection release message sent by a serving MSC/VLR, wherein, theconnection release message comprises an identity of the UE and identityinformation of the LTE PLMN and the transmitter is further configured tosend the identity of the UE and the identity information of the LTE PLMNto the LTE base station.

In combination with the eighth aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, when the serving MSC/VLR is a registered MSC/VLR ofthe UE, the identity of the UE and the identity information of the LTEPLMN is acquired from a registration information of the UE by theserving MSC/VLR; or, when the serving MSC/VLR is not a registeredMSC/VLR of the UE, the identity of the UE and the identity informationof the LTE PLMN is acquired from the registered MSC/VLR by the servingMSC/VLR.

In combination with the eighth aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, the LTE base station is a base station which providesaccess service when the UE initiates the CSFB service; and the LTE basestation further comprises: a storage, configured to store the identityof the UE and the identity information of the LTE PLMN when the UEinitiates the CSFB service in the LTE PLMN.

In combination with the eighth aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, the processor is further configured to delete thestored identity of the UE and the identity information of the LTE PLMN.

In the ninth aspect of the present application, a UE is provided,comprising: a registering unit, configured to perform a combinedregistration in an LTE PLMN; a fallback unit, configured to initiate aCSFB service to fall back to a 2G/3G network; a receiving unit,configured to receive an equivalent PLMN list in the 2G/3G network; anadding unit, configured to add identity information of the LTE PLMN tothe equivalent PLMN list received by the receiving unit; and a selectingunit, configured to perform, according to the equivalent PLMN listmodified by the adding unit, a PLMN selection when the CSFB serviceends.

In combination with the ninth aspect of the present application, in aprobable way of implementation, the selecting unit is configured to:select, according to the equivalent PLMN list modified by the addingunit, the LTE PLMN in priority.

In combination with the ninth aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, the selecting unit is configured to: select,according to the equivalent PLMN list modified by the adding unit, acell on a frequency band corresponding to LTE frequency bandinformation; and select the LTE PLMN in priority from available PLMNsfor the cell; wherein, the LTE frequency band information is informationof an LTE frequency band selected by the UE when the UE initiates acombined registration to the LTE PLMN.

In combination with the ninth aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, the selecting unit is specifically configured to:select, according to the equivalent PLMN list modified by the addingunit, a cell on a frequency band corresponding to LTE frequency bandinformation; and select the LTE PLMN in priority from available PLMNsfor the cell; wherein, the LTE frequency band information is receivedfrom the 2G/3G network by the UE.

In the tenth aspect of the present application, a UE is provided,comprising: a registering unit, configured to perform a combinedregistration in an LTE PLMN; a selecting unit, configured to perform aPLMN selection on a frequency band corresponding to LTE frequency bandinformation when a CSFB service ends, wherein, the LTE frequency bandinformation is information of an LTE frequency band selected by the UEwhen the UE initiates a combined registration to the LTE PLMN.

In combination with the tenth aspect of the present application, in aprobable way of implementation, the selecting unit is configured to:select a cell on the frequency corresponding to the LTE frequencyinformation, and select the LTE PLMN in priority from available PLMNsfor the cell.

In combination with the tenth aspect of the present application and theaforementioned probable ways of implementation, in another probable wayof implementation, the UE further comprises: a storing unit, configuredto store the LTE frequency band information when the CSFB service isinitiated the and a CS domain is fallen back to, wherein the selectingunit is further configured to acquire the LTE frequency information fromthe storing unit when the CSFB service ends.

In the eleventh aspect of the present application, a 2G/3G base stationis provided, configured to provide service for a CSFB service. The 2G/3Gbase station comprises: a receiving unit, configured to receive aconnection release message sent by a serving MSC/VLR, wherein theconnection release message comprises identity information of an LTE PLMNregistered when a UE initiates a CSFB service; a selecting unit,configured to select, according to the identity information of the LTEPLMN which is received by the receiving unit, target frequency bandinformation, wherein the target frequency band information is configuredto indicate the UE to select a cell for residing on a frequency bandcorresponding to the target frequency band information; and a sendingunit, configured to send the target frequency band information selectedby the selecting unit to the UE.

In combination with the eleventh aspect of the present application, in aprobable way of implementation, the sending unit is configured to: sendpriority information to the UE, wherein the priority informationcomprises the frequency band information.

In the twelfth aspect of the present application, an LTE base station,comprising: a receiving unit, configured to receive a connectionestablishment request message sent by a UE when a CSFB service ends,wherein, the connection establishment request message comprises anidentity of the UE; a selecting unit, configured to select, according tothe identity of the UE and identity information of LTE PLMN registeredwhen the UE initiates the CSFB service, which are received by thereceiving unit, the LTE PLMN corresponding to the identity informationof the LTE PLMN.

In combination with the twelfth aspect of the present application, in aprobable way of implementation, the receiving unit is configured to:receive and store the identity of the UE and the identity information ofthe LTE PLMN, which are sent by a 2G/3G base station, wherein, the 2G/3Gbase station is a base station which provides a service for the CSFBservice.

In combination with the twelfth aspect of the present application andthe aforementioned probable ways of implementation, in another probableway of implementation, the receiving unit is further configured to:before receiving the identity of the UE and the identity information ofthe LTE PLMN sent by a 2G/3G base station, receive, by the 2G/3G basestation, a connection release message sent a serving MSC/VLR, whereinthe connection release message comprises the identity of the UE and theidentity information of the LTE PLMN and the 2G/3G base station sendsthe identity of the UE and the identity information of the LTE PLMN tothe 2G/3G base station.

In combination with the twelfth aspect of the present application andthe aforementioned probable ways of implementation, in another probableway of implementation, when the serving MSC/VLR is a registered MSC/VLRof the UE, the identity of the UE and the identity information of theLTE PLMN is acquired from a registration information of the UE by theserving MSC/VLR; or, when the serving MSC/VLR is not a registeredMSC/VLR of the UE, the identity of the UE and the identity informationof the LTE PLMN is acquired from the registered MSC/VLR by the servingMSC/VLR.

In combination with the twelfth aspect of the present application andthe aforementioned probable ways of implementation, in another probableway of implementation, the LTE base station is a base station whichprovides an access service when the UE initiates the CSFB service; andthe LTE base station further comprises: a storing unit, configured tosave the identity of the UE and the identity information of the LTE PLMNwhen the UE initiates the CSFB service in the LTE PLMN.

In combination with the twelfth aspect of the present application andthe aforementioned probable ways of implementation, in another probableway of implementation, the LTE base station further comprises: adeleting unit, configured to delete the stored identity of the UE andthe identity information of the LTE PLMN.

Compared with a method in the prior art, which randomly assigns a UE toreturn to any of a neighboring LTE network, a method and device forselecting an LTE network, provided in embodiments in the presentapplication, which comprises when a UE initiates a connectionestablishment request to an LTE network after a CSFB service ends,determining, by matching an identity sent by the UE with the storedidentity of the UE, an LTE PLMN registered by the UE when the UEinitiates the CSFB, can assign the UE to return to the LTE PLMNregistered when the CSFB is initiated, which not only reduces anunnecessary inter-PLMN switch, but also recovers a data servicesuspended in the previously registered LTE PLMN, thereby improvingservice efficiency and promoting user experience.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to illustrate the technical solution in the embodiments of thepresent application more clearly, a brief description to the drawingsrequired in the embodiments or the prior art will be made below.Apparently, the drawings described below are merely some embodiments ofthe present application, and other drawings could be achieved based onthese drawings by those of ordinary skill in the art without creativeefforts.

FIG. 1 is a flowchart of a method for selecting an LTE network in anembodiment of the present application;

FIG. 2 is a flowchart of a method for selecting an LTE network inanother embodiment of the present application;

FIG. 3 is a flowchart of a method for selecting an LTE network inanother embodiment of the present application;

FIG. 4 is a flowchart of a method for selecting an LTE network inanother embodiment of the present application;

FIG. 5 is a flowchart of a method for selecting an LTE network inanother embodiment of the present application;

FIG. 6 is a flowchart of a method for selecting an LTE network inanother embodiment of the present application;

FIG. 7 is a schematic view of a composition of a UE in anotherembodiment of the present application;

FIG. 8 is a schematic view of a composition of a UE in anotherembodiment of the present application;

FIG. 9 is a schematic view of a composition of a 2G/3G base station inanother embodiment of the present application;

FIG. 10 is a schematic view of a composition of an LTE base station inanother embodiment of the present application;

FIG. 11 is a schematic view of a composition of a UE in anotherembodiment of the present application;

FIG. 12 is a schematic view of a composition of a UE in anotherembodiment of the present application;

FIG. 13 is a schematic view of a composition of a 2G/3G base station inanother embodiment of the present application;

FIG. 14 is a schematic view of a composition of an LTE base station inanother embodiment of the present application.

DESCRIPTION OF EMBODIMENTS

A clear description of technical solutions of the embodiments of thepresent application will be given below, in combination with theaccompanying drawings in the embodiments of the present application.Apparently, the embodiments described below are just a part, but notall, of the embodiments of the present application. All of otherembodiments, obtained by those skilled in the art based on theembodiments of the present application without any inventive efforts,fall into the protection scope of the present application.

In the specification, an LTE network described is an Evolved UMTSTerritorial Radio Access Network (an English full name is Evolved UMTSTerritorial Radio Access Network, and an English abbreviation isE-UTRAN, wherein, an English full name of UMTS is Universal MobileTelecommunications System). A 2nd Generation (2G) network is a GSM/EDGERadio Access Network (an English full name is GSM/EDGE Radio AccessNetwork, an English abbreviation is GERAN, wherein, a Chinese full nameof GSM is Global System of Mobile communication, an English full name isGlobal System of Mobile communication, an English full name of EDGE isEnhanced Data Rate for GSM Evolution). A 3rd Generation (3G) network isUTRAN network. A PLMN of an LTE network only provides a PS domainservice, while in a 2G/3G network, not only a PLMN providing a CS domainservice but also a PLMN providing PS domain service are included.

In an embodiment of the present application, a user equipment (UE forshort) may be any of the following ones, and the UE may be static ormobile. A Static UE may include a terminal, a mobile station, asubscriber unit, a station or the like. A Mobile UE may include acellular phone, a personal digital assistant (PDA), a wireless modem, awireless communication device, a handheld device, a laptop computer, acordless phone, a wireless local loop (WLL) station or the like. Theaforementioned UE may be distributed in a whole wireless network.

In order to facilitate the understanding for those skilled in the art,specific application examples are illustrated below. It shall be notedthat, in an embodiment of the present application, an LTE base stationmay be a base station which provides an access service of an LTEnetwork, such as eNodeB. A 2G/3G base station may be a base station(BSS) in a 2G network, or a radio network subsystem (RNS) in a 3Gnetwork. A mobile management network element may be any one of a MobileSwitching Centre (MSC)/Visitors Location Register (VLR), or a MobilityManagement Entity (MME), or a Serving GPRS Support Node (SGSN), whereina MSC and a VLR are generally combined as an identical network element,which is named as MSC/VLR or VLR for short.

Since an LTE network only supports a PS data service, a UE needs toperform a Circuit Domain Fall Back (CSFB) flow to make the UE fall backfrom the LTE network to a 2G/3G network if the UE initiates or receivesa circuit domain service (including a voice call, a supplementaryservice, a location service or the like) while performing data serviceor in an idle state in the LTE network, in order that the UE completes acircuit domain service in the 2G/3G network. When a CS service ends (arelease of an underlying connection established by the UE in a 2G/3Gnetwork due to a CSFB service means the end of a circuit domainservice), a terminal needs to return to an LTE network to go on with adata service in the LTE network. In an embodiment of the presentapplication, a CSFB service specifically refers to a CS serviceperformed by a UE which resides in an LTE network when the UE initiatinga CSFB flow and falling back to a 2G/3G network as a CS service needs tobe performed, and the CSFB service includes an uplink CSFB service and adownlink CSFB service, such as a downlink CSFB service triggered when aUE receives a voice call paging, an uplink CSFB service triggered by anactive voice call or the like. In an embodiment of the presentapplication, a source MSC/VLR is an MSC/VLR to which the UE issuccessfully registered in a combined registration flow, which is also aserving MSC/VLR of the UE when residing in an LTE network after asuccessful combined registration and which is also called as aregistered MSC/VLR. A serving MSC/VLR is an MSC/VLR which provides aservice for a UE to perform a CS service when the UE initiates a CSFBflow and falls back to a 2G/3G network, which is also called as a targetMSC/VLR.

In an inner part of a UE, the inner part of the UE may be divided intoan access stratum (AS) and a non-access stratum (NAS) according todifferences of objects of message which are processed and controlled.The AS is responsible for receiving an RR/RRC connection releasemessage, selecting, according to a frequency band, a suitable cell andresiding, reading the cell system broadcast message, acquiring availablePLMN information and then reporting it to the NAS. The NAS determineswhether to perform a PLMN selection according to the available PLMNinformation reported by the AS.

A method for selecting an LTE network is provided in an embodiment ofthe present application. As shown in FIG. 1, the method comprises thefollowing steps.

101, an LTE base station receives a connection establishment requestmessage sent by a UE when a CSFB service ends, and the connectionestablishment request message comprises an identity of the UE.

Alternatively, an LTE base station provides an LTE access service forthe UE. The UE registers to an LTE base station when a CSFB isinitiated. When UE initiates a CSFB, an LTE base station may store anidentity of the UE and identity information of an LTE PLMN registered bythe UE, so that when the CSFB service of the UE ends and when aconnection establishment request message sent by the UE, which includesthe identity of the UE, is received, the LTE PLMN registered when theCSFB is initiated is selected for the UE according to the identity ofthe UE and the stored identity information of the LTE PLMN registeredwhen the UE initiates the CSFB service.

Alternatively, when a CSFB service initiated by a UE ends, a servingMSC/VLR may send an identity of the UE and identity information of anLTE PLMN registered by the UE to a 2G/3G base station which provides anaccess service in CS domain for the UE, so that the 2G/3G base stationtransmits the identity of the UE and the identity information of the LTEPLMN registered by the UE to neighboring LTE base stations capable ofproviding an LTE access service for the UE when the CSFB service ends.These neighboring base stations include the LTE base station registeredwhen the UE initiates the CSFB. The LTE base station stores the identityof the UE and the identity information of the LTE PLMN registered by theUE, which are sent by the 2G/3G base station. In this way, when an LTEbase station receives the connection establishment request message sentby the UE, which includes the identity of the UE, the LTE PLMNregistered when the CSFB is initiated may be selected for the UEaccording to the identity of the UE and the stored identity informationof the LTE PLMN registered by the UE. The 2G/3G base station may obtainin advance a base station which is adjacent to the 2G/3G base stationand which may provide an LTE access service, for example, obtaining aneighboring eNodeB based on network configuration or using an automaticneighbor relation, and the identity of the UE and the identityinformation of the LTE PLMN may be sent to each neighboring base stationwhich provides an LTE access service. Since a CSFB is initiated, by aUE, when an LTE service is performed in an LTE base station, a nearby2G/3G base station, which is capable of providing CS domain, would beselected, and thereby the LTE base station previously registered by theUE is adjacent to the 2G/3G base station which performs the CSFBservice. The LTE base station receives and stores the identity of the UEand the identity information of the LTE PLMN, which are sent by the2G/3G base station. In this way, when the UE searches a suitable cell toreturn to an LTE network, an LTE base station may determine and selectthe identity information of the LTE PLMN when the UE initiates the CSFBservice if the UE enters a service area of the LTE base station.

It shall be noted that, if the serving MSC/VLR is a registered MSC/VLRof the UE, the serving MSC/VLR acquires an identity of the UE andidentity information of the LTE PLMN registered by the UE fromregistration information of the UE. If the serving MSC/VLR is not aregistered MSC/VLR of the UE, the serving MSC/VLR acquires an identityof the UE and identity information of the LTE PLMN registered by the UEfrom a registered MSC/VLR of the UE.

An identity of the UE may be a System Architecture Evolution (SAE)Temporary Mobile Subscriber Identity (S-TMSI), an International MobileSubscriber Identity (IMSI) or Temporary Mobile Subscriber Identity(TMSI), which is not limited in an embodiment of the presentapplication. Identity information of the LTE PLMN registered by the UEmay be a registered LTE PLMN identity (ID); it may also be a GloballyUnique Temporary Identity (GUTI) including a registered LTE PLMN ID; itmay also be a Tracking Area Identity (TAI) including registered LTE PLMNID; and it may also be an E-UTRAN Cell Global Identity (ECGI) includinga registered LTE PLMN ID, which is not limited in an embodiment of thepresent application.

Wherein, the connection establishment request message is sent when theCSFB service initiated by the UE ends. An LTE base station may be a basestation which provides an LTE access service, such as an eNodeB. An LTEbase station may be shared by at least two LTE PLMNs, that is to say, anLTE base station may provide LTE access services for at least two LTEPLMNs, for example, an LTE base station may provide an LTE accessservice for both PLMN1 and PLMN2.

102, the LTE base station selects the LTE PLMN corresponding to theidentity information of the LTE PLMN according to the identity of the UEand identity information of an LTE PLMN registered when the UE initiatesthe CSFB service.

Since the LTE base station may obtain the identity of the UE and theidentity information of the LTE PLMN, a match may be performed accordingto a received UE identity which is sent by the UE and a stored UEidentity to determine the identity information of the LTE PLMNcorresponding to the UE identity. The LTE base station may uniquelydetermine, according to the identity information of the LTE PLMN, thecorresponding LTE PLMN and select the LTE PLMN to provide an LTE servicefor the UE.

Compared with a method, defined in the prior art, for returning to anLTE network after the CSFB, a method for selecting an LTE network, whichis provided in an embodiment of the present application, comprising whena UE initiates a connection establishment request to an LTE network whena CSFB service ends, determining and selecting, by matching the UEidentity sent by the UE with the stored identity of the UE, an LTE PLMNregistered when the UE initiates the CSFB and selecting, can ensure thatthe UE returns to the LTE PLMN registered when the CSFB is initiated,which not only reduces an unnecessary inter-PLMN switch, but alsorecovers a data service suspended in the previously registered LTE PLMN,thereby improving the service efficiency and promoting the userexperience.

Another method for selecting an LTE network is provided in an embodimentof the present application. As shown in FIG. 2, the method comprises:

201, A UE initiates a combined registration and is successfullyregistered to a PLMN1 supporting an LTE network and a PLMN2 supporting a2G/3G network.

The UE which resides in an E-UTRAN and supports a CSFB needs to initiatea combined registration flow to realize a simultaneous registration to aPS domain of an EPC network and a CS domain of a 2G/3G network. When theUE is registered to a PS domain network (LTE PLMN1), a source MSC/VLR inPLMN2 may acquire the identity of the UE and the PLMN ID1 of the PLMN1.

In a combined registration flow, a network side selects the sourceMSC/VLR for the UE. When the UE is registered to the CS domain network(CS PLMN2), a Mobile Management Entity (MME) selects a source MSC/VLRwhich is capable of providing service for the UE and sends a locationupdate request to the selected source MSC/VLR to establish an SGsassociation. The source MSC/VLR sends a registration request to a HomeLocation Register (HLR) and acquires CS domain subscription data of theUE to realize a registration of the UE in a CS domain. Alternatively,under a scenario that an MSC resource pool (MSC pool) is not deployed,an MME selects a servable MSC/VLR according to current locationinformation of the UE; under a scenario that an MSC resource pool (MSCpool) is deployed, an MME selects a serving MSC/VLR from the MSC poolaccording to current location information of the UE and an InternationalMobile Subscriber Identity (IMSI) hash table.

202, the UE initiates a CSFB in the PLMN1, and successfully falls backto a 2G/3G network of the PLMN2.

When a combined registration is successfully realized, a CSFB servicemay be normally initiated. In the flow that a UE initiates an uplink anda downlink CSFB, an MME in an LTE network selects a CS service PLMN IDfor the UE and sends the selected CS PLMN ID to an LTE base station(eNodeB) in the LTE network to inform that the LTE base station (eNodeB)should fall the UE back to a CS network corresponding to the CS PLMN ID.A CS domain service may be initiated when the UE switches to the 2G/3Gnetwork. For example, in an initiated CS voice call establishment flow,a UE may send a CSFB indication to a serving MSC/VLR. The CSFBindication is used for indicating that this voice call is triggered as aCSFB is performed in the LTE network. When a CS voice call connection isestablished successfully, a UE performs a voice call.

203, a source MSC/VLR sends an identity of the UE and a PLMN ID1 to aserving MSC/VLR.

The step 203 is an optional step. If a serving MSC/VLR of the UE in a2G/3G network to which the UE falls back is the source MSC/VLR, the step203 need not to be performed. Only when a serving MSC/VLR of the UE isnot the source MSC/VLR registered in the step 201, the step 203 isperformed.

In the combined registration process of the step 201, a source MSC/VLRmay acquire an identity of the UE from a registration information. Forexample, in the combined registration process, an MME will send an IMSIof the UE to a source MSC/VLR, or an MME may also send a SAE TemporaryMobile Subscriber Identity (S-TMSI) of the UE to a source MSC/VLR.Furthermore, a source MSC/VLR may acquire a PLMN ID1 registered by theUE from registration information. For example, in a combinedregistration process, an MME will send an MME name to a source MSC/VLR,and a PLMN ID1 registered by a UE is included in the MME name. Or, in acombined registration flow, an MME may send a Tracking Area Identity(TAI) or an E-UTRAN Cell Global Identity (ECGI) to a source MSC/VLR, anda PLMN ID1 registered by the UE is included in the TAI or the ECGI.

In the embodiment, if the UE enters the service range of anotherMSC/VLR, i.e., a serving MSC/VLR, when falling back to a 2G/3G network,the UE will report location information of a source MSC/VLR to a servingMSC/VLR during the location update process with the serving MSC/VLR.Then, the serving MSC/VLR sends, according to the location positionreported by the UE, a Mobile Application Part (MAP) SEND IDENTIFICATIONmessage to the source MSC/VLR on a request to acquire an identity of theUE and a registered PLMN ID1. The source MSC/VLR sends the identity ofthe UE and the registered PLMN ID1, which are acquired in the step 201,to the serving MSC/VLR in an MAP SEND IDENTIFICATION response message.

204, the UE performs a CS domain service in the PLMN2.

A CS domain service after the CSFB may include initiating or receiving avoice call, a supplementary service, a location service or the like.

205, when the CS domain service of the UE ends, a serving MSC/VLR sendsa first connection release message to a 2G/3G base station, and thefirst connection release message includes a CSFB indication, a UEidentity and a PLMN ID1, that is to say, the 2G/3G base station obtainsthat the CSFB service of the UE ends.

When a CS domain service of a UE ends, a serving MSC/VLR initiates aconnection release flow to a base station, and a CSFB indication, a UEidentity and a PLMN ID1 are carried in a first connection releasemessage. The CSFB indication is used for indicating that a current CSdomain service of a UE is caused by a CSFB, and when the CS domainservice ends, the UE needs to be redirected to return to an LTE network.

A UE identity sent from a serving MSC/VLR to a 2G/3G base station may bean S-TMSI, an IMSI or a Temporary Mobile Subscriber Identity (TMSI) of aUE, which is not limited in an embodiment of the present application.Identity information of a registered LTE PLMN, which is sent from aserving MSC/VLR to a 2G/3G base station, may be a registered LTE PLMNidentity (ID); it may also be a Globally Unique Temporary Identity(GUTI) which includes a registered LTE PLMN ID; it may also be aTracking Area Identity (TAI) which includes a registered LTE PLMN ID; itmay also includes an E-UTRAN Cell Global Identity (ECGI) which includesa registered LTE PLMN ID. In the embodiment, it is only taken as anexample that identity information of a registered LTE PLMN is a PLMNID1, and the identity information of a registered LTE PLMN in otherforms will not be described redundantly in an embodiment of the presentapplication.

206, the 2G/3G base station sends the identity of the UE and the PLMNID1 to neighboring base stations which provide LTE access services, andthe neighboring base stations which provide LTE access services includethe LTE base station which provides an LTE access service for the UEwhen the UE initiates the CSFB.

For example, the 2G/3G base station may send the acquired identity ofthe UE and the registered LTE PLMN ID1 to the neighboring base stationswhich provide LTE access services through a flow of Radio Access NetworkInformation Management (RIM), and the LTE base stations store thereceived identity of the UE and PLMN ID1. The 2G/3G base station mayobtain the neighboring base stations which provide LTE access servicesthrough configuration of a network management system, and may alsodiscover the neighboring base stations which provide LTE access servicesthrough an automatic neighbour discovery flow.

Furthermore, in order to avoid occupying excessive storage resources ofan LTE base station, the identity of the UE and the identity informationof the LTE PLMN registered by the UE may not be permanently stored.Alternatively, when an LTE base station obtains that a UE initiates aCSFB flow, a timer may be started. When the timer expires, the storedidentity of the UE and LTE PLMN ID1 registered by the UE are deleted,wherein, the timing of the timer may be preset according to factors suchas a size of storage space and a degree of service busy of an LTE basestation, a priority of a UE and the like, which is not limited in thepresent application. Or, the stored identity of the UE and LTE PLMN ID1registered by the UE may also be deleted by adopting other triggerconditions, for example, when a stored identity of a UE and identityinformation of an LTE PLMN registered by UE reach a certain capacity orreach a certain quantity, an earliest stored identity of a UE andidentity information of LTE PLMN registered by a UE are deleted untilthe capacity or quantity of stored identities of the UE and identityinformation of LTE PLMN are lower than or equal to a stored presetcapacity or quantity.

207, the 2G/3G base station selects LTE frequency band (Frequency)information according to a CSFB indication.

It belongs to the prior art that a 2G/3G base station selects an LTEfrequency band for the UE when a first connection release message isreceived. The determined LTE frequency band information may be LTEfrequency band information supported by a registered LTE PLMN; or it maybe LTE frequency band information corresponding to the PLMN2; or it mayalso be LTE frequency band information supported by other PLMNs, whichwill not introduced in details in an embodiment of the presentapplication.

208, the 2G/3G base station sends a second connection release message tothe UE, wherein, the second connection release message comprises the LTEfrequency information selected in the step 207.

The first connection release message and the second connection releasemessage involved in the specification of the application may be a RadioResource (RR) connection release message, or a Radio Resource Control(RRC) connection release message, or other messages which are used forassisting the release of a radio resource. If a 2G/3G base station is aBSS, the BSS sends an RR connection release message to a UE. An RRconnection release message includes a redirection indication, which isused for indicating the UE to perform redirection and to return to anLTE network when the UE releases an RR connection. And LTE frequencyband information is taken as the content of the redirection indication,for indicating the UE to perform redirection and to return to an LTEnetwork corresponding to an LTE frequency band. If the base station isan RNS, the RNS sends an RRC connection release message to the UE. TheRRC connection release message includes a redirection indication forindicating the UE to perform redirection and to return to an LTE networkwhen the UE releases an RRC connection. And LTE frequency bandinformation is taken as the content of the redirection indication, forindicating the UE to perform redirection and to return to an LTE networkcorresponding to an LTE frequency band.

209, the UE searches a suitable cell on the LTE frequency for residing.

When a current RR/RRC connection is released, a UE searches a suitablecell on an LTE frequency band according to LTE frequency informationassigned in a redirection indication, and resides in the suitable cellsearched on the LTE frequency band. The suitable cell is a cell wherethe UE may reside and may acquire a normal service. In a practicalapplication, it may occur that a UE can not acquire the normal servicesin a searched cell on an LTE frequency band (for example, only anemergency service can be acquired), i.e., it is a non-suitable cell. Inthis case, the UE may search a suitable cell again on all frequencybands, which is not taken into account in embodiments of the presentapplication and will not describe redundantly.

It shall be noted that, in this step, a UE probably enters anyneighboring base station of the current 2G/3G base station, whichprovides an LTE access service and which includes an LTE base stationwhen the UE initiates a CSFB previously. For the convenience ofdescription, the LTE base station where the UE initiates a CSFB beforeentry is taken as an example in this step, as well as steps 210 and 211below. If the UE enters other neighboring base stations which provideLTE access services, the neighboring base stations perform the sameactions as that performed by the LTE base station.

210, the UE sends a connection establishment request message to the LTEbase station, and the connection establishment request message includesthe identity of the UE.

The identity of the UE may be a System Architecture Evolution (SAE)Temporary Mobile Subscriber Identity (S-TMSI), an International MobileSubscriber Identity (IMSI) or a Temporary Mobile Subscriber Identity(TMSI), which is not limited in an embodiment of the presentapplication.

It shall be noted that, in this step, if the UE enters other neighboringbase station which provides an LTE access service, the UE sends theconnection establishment request message which includes the identity ofthe UE to the base station.

211, the LTE base station determines the PLMN ID1 registered by the UEby matching the identity of the UE which is included in the connectionestablishment request message with the stored identity of the UE, andselects a PLMN corresponding to the PLMN ID1 registered by the UE toprovide an LTE access service for the UE.

In order to return to the LTE network to perform a PS service, the UEinitiates a joint Tracking Area Updating (TAU) flow, which may initiatea connection establishment flow in the PLMN1 and recover a suspendeddata service in the PLMN1. Through the step 206, the LTE base stationhas already acquired and stored the identity of the UE and the identityinformation of the LTE PLMN corresponding to the identity of the UE,which is registered by the UE, as a result, the PLMN ID1 registered whenthe UE initiates the CSFB may be queried in this step.

Specifically, the connection establishment request message sent by theUE may also include the identity information of the LTE PLMN, which isselected by the UE. The LTE base station may match the identity of theUE and stored identities of UE, and determine, by comparison, whetherthe identity information of the LTE PLMN, which is selected by the UE,is the same as the stored identity information of the LTE PLMNregistered by the UE. If the two are different, the identity informationof the registered LTE PLMN may by replaced, by the LTE base station,with the identity information of the LTE PLMN in the connectionestablishment request message, and send it to the MME connected with theLTE base station to complete a TAU flow.

The method for selecting an LTE network, which is provided by anembodiment of the present application, comprising: when a UE initiates aconnection establishment request message to an LTE network, an LTE basestation determining and selecting, by matching an identity of the UEsent by the UE with a stored identity of the UE, identity information ofan LTE PLMN registered by the UE when the UE initiates a CSFB, canensure that the UE returns to the LTE PLMN registered when the CSFB isinitiated, which not only reduces an unnecessary inter-PLMN switch, butalso recovers a data service suspended in the previously registered LTEPLMN, thereby improving the service efficiency and promoting the userexperience.

Another method for selecting an LTE network is provided in an embodimentof the present application. As shown in FIG. 3, the method comprises thefollowing steps.

301, a UE initiates a combined registration and is successfullyregistered to a PLMN1 supporting an LTE network and a PLMN2 supporting a2G/3G network.

302, the UE initiates a CSFB in the PLMN1, and successfully falls backto a 2G/3G network of the PLMN2.

Wherein, similar to the embodiment shown in FIG. 2, the steps 301-302belong to the prior art, and will not described redundantly in detailsin the embodiment of the present application.

303, an LTE base station stores an identity of the UE and an LTE PLMNID1 registered by the UE.

The LTE base station stores the identity of the UE and the identityinformation of the LTE PLMN registered by the UE in order to select theLTE network registered when the CSFB is initiated for the UE when the UEperforms an LTE network selection after a CSFB service. In order toavoid occupying excessive storage resources of an LTE base station, theidentity of the UE and the identity information of the LTE PLMNregistered by the UE may not be permanently stored. Alternatively, whenan LTE base station obtains that UE initiates a CSFB flow, a timer maybe started. When the timer expires, the stored identity of the UE andLTE PLMN ID1 registered by the UE are deleted, wherein, the timing ofthe timer may be preset according to factors such as a size of storagespace and a degree of service busy of an LTE base station, a priority ofa UE and the like, which is not limited in the present application. Or,the stored identity of the UE and LTE PLMN ID1 registered by the UE mayalso be deleted by adopting other trigger conditions, for example, whena stored identity of a UE and identity information of an LTE PLMNregistered by a UE reach a certain capacity or reach a certain quantity,an earliest stored identity of a UE and identity information of LTE PLMNregistered by a UE are deleted until the capacity or quantity of storedidentities of the UE and identity information of LTE PLMN are lower thanor equal to a stored preset capacity or quantity.

304, when the CSFB service of the UE ends, a serving MSC/VLR sends afirst connection release message to the 2G/3G base station, wherein, thefirst connection release message includes a CSFB indication.

Wherein, the CSFB indication is used for indicating the UE that the CSdomain service which ends currently is caused by a CSFB, and when the CSdomain service ends, the UE needs to return to an LTE network.

305, the 2G/3G base station sends a second connection release message tothe UE, and the second connection release message includes LTE frequencyband information.

306, a suitable cell of the LTE base station is searched by the UE on anLTE frequency band for residing.

307, the UE sends a connection establishment request message to the LTEbase station, wherein, the connection establishment request messageincludes the identity of the UE.

In the embodiment, the steps 304-307 belong to the prior art, and willnot be described redundantly in details in the embodiment of the presentapplication.

308, the LTE base station determines the PLMN ID1 registered by the UEby matching the identity of the UE which is included in the connectionestablishment request message with the stored identity of the UE, andselects a PLMN corresponding to the PLMN ID1 registered by the UE toprovide an LTE access service for the UE.

Wherein, the LTE base station may select, according to the storedidentity of the UE and identity information of the LTE PLMN registeredby the UE in the step 303 and the identity of the UE identity includedin the connection establishment request message, a PLMN corresponding tothe registered PLMN ID1 for the UE to provide an LTE access service forthe UE. The specific way of implementation in the step 308 is similar tothe way of implementation in the step 211 in an embodiment correspondingto FIG. 2. The corresponding contents in the step 211 may be referred toand will not be described redundantly in the embodiment of the presentapplication here.

The method for selecting an LTE network, which is provided in theembodiment of the present application, comprises that when a CSFBservice of a UE ends, a 2G/3G base station sends an identity of the UEand identity information of an LTE PLMN registered by the UE to an LTEbase station, so that when the UE initiates a connection establishmentrequest message to an LTE network, the LTE base station may determine,according to the identity of the UE which is sent by the UE, theidentity information of the LTE PLMN registered by the UE when the UEinitiates the CSFB, can ensure that the UE returns to the LTE PLMNregistered when the CSFB is initiated, which not only reduces anunnecessary inter-PLMN switch, but also recovers a data servicesuspended in the previously registered LTE PLMN, thereby improvingservice efficiency and promoting user experience.

Another method for selecting an LTE network is provided in an embodimentof the present application. A UE stores identity information of an LTEPLMN registered when a CSFB is initiated, and uses the stored identityinformation of the LTE PLMN to update an equivalent PLMN list. As shownin FIG. 4, the method comprises the following steps.

401, A UE performs a combined registration in an LTE PLMN.

The UE is simultaneously registered to a 2G/3G network and an LTEnetwork. A data service may be performed in the LTE network. When a CSdomain service needs to perform, a CSFB flow may be initiated to fallback to the 2G/3G network.

402, the UE initiates a CSFB service to fall back to a 2G/3G network.

When the CSFB service is initiated to fall back to the 2G/3G network,the UE may store identity information of the registered LTE PLMN in thestep 401. It shall be noted that, if the UE has already saved theidentity information of the registered LTE PLMN in the registration flowof the step 401, for example, a GUTI including registered LTE PLMN ID ora TAI including registered LTE PLMN ID has already been stored, the UEdoes not need to repeatedly save the identity information of theregistered LTE PLMN in this step. In this way, the identity informationof the LTE PLMN in the steps 403 and 404 below are the stored identityinformation of the LTE PLMN in the step 401.

The stored identity information of the registered LTE PLMN may be aregistered LTE PLMN identity (ID); it may also be a Tracking AreaIdentity (TAI) including registered LTE PLMN ID; and it may also be aGlobally Unique Temporary Identity (GUTI) including registered LTE PLMNID.

Alternatively, the UE may store LTE frequency band information selectedwhen the combined registration is initiated to the LTE PLMN in the step401. An LTE frequency band corresponding to the LTE frequency bandinformation is an LTE frequency band selected when the CSFB is initiatedin this step. It shall be noted that, the registered LTE PLMN in thestep 401 may support several LTE frequency bands.

403, the UE receives an equivalent PLMN list in the 2G/3G network, andadds the identity information of the LTE PLMN to the equivalent PLMNlist.

If the UE falls back to a new Location Area (LA) of the 2G/3G networkwhen the CSFB flow is initiated, the UE will initiate a Location AreaUpdate (LAU) flow to a CS domain of the serving MSC/VLR. In the LocationUpdate flow, a serving MSC/VLR may send an equivalent PLMN list to a UE,so that the UE in an idle state performs cell selection/reselection andPLMN selection.

Alternatively, if the UE falls back to one new routing area (RA) of a2G/3G network when a CSFB flow is initiated, the UE will initiate aRouting Area update flow to a PS domain of the SGSN. In the Router Areaupdate flow, the SGSN may send an equivalent PLMN list to a UE, so thatthe UE in an idle state performs cell selection/reselection and PLMNselection.

Further, if a UE simultaneously initiates a Location Update flow of a CSdomain and a Router Area update flow of a PS domain, both the servingMSC/VLR and the SGSN may send a same equivalent PLMN list to the UE.

When an equivalent PLMN list in a 2G/3G network is received, a UE willstore the received equivalent PLMN list to replace the previously storedequivalent PLMN list. Further, the UE adds the stored identityinformation of the LTE PLMN in the step 402 to the equivalent PLMN list.It shall be noted that, adding the identity information of the LTE PLMNto the equivalent PLMN list generally means adding the PLMN ID to theequivalent PLMN list, for example, the PLMN ID included in a GUTI isadded to the equivalent PLMN list. It shall be noted that, if a UE doesnot receive an equivalent PLMN list when the UE falls back to a 2G/3Gnetwork, the UE does not need to add the stored identity information ofthe LTE PLMN in the step 402 to the stored equivalent PLMN list, as thestored equivalent PLMN list has already included the stored identityinformation of the LTE PLMN in the step 402.

404, when the CSFB service is ends, a PLMN selection is performedaccording to the equivalent PLMN list.

The stored identity information of the LTE PLMN has already been addedto the equivalent PLMN list through the step 403. A suitable cell forresiding may be selected according to the updated equivalent PLMN listwhen a PLMN selection is performed. That is to say, a suitable cell forresiding is selected according to the equivalent PLMN list including theidentity information of the LTE PLMN, and an LTE PLMN is selected fromavailable PLMNs of the selected suitable cell. Further, that a PLMNselection is performed according to the equivalent PLMN list mayinclude: an LTE PLMN corresponding to the identity information of theLTE PLMN is selected in priority according to the equivalent PLMN list.That is to say, a PLMN corresponding to the stored identity informationof the LTE PLMN is selected in priority from all available PLMNs of theselected suitable cell. Further, the selecting an LTE PLMN in prioritymay include: a suitable cell for residing is selected, according to theequivalent PLMN list, on a frequency band corresponding to LTE frequencyband information, and a PLMN corresponding to the stored identityinformation of the LTE PLMN is selected in priority from the availablePLMNs of the suitable cell.

Alternatively, the LTE frequency information may be information of anLTE frequency band selected when the UE initiates combined registrationto the LTE PLMN. When the UE initiates the CSFB service and falls backto a 2G/3G network, the UE may also store the LTE frequency informationselected when the combined registration is initiated to the LTE PLMN. Inthis way, when a return to an LTE is needed after the CSFB service, asuitable cell for residing may be selected, according to the equivalentPLMN list, on a frequency band corresponding to the LTE frequency bandinformation, and a PLMN corresponding to the stored identity informationof the LTE PLMN is selected in priority from the available PLMNs of thesuitable cell.

Alternatively, the LTE frequency band information may be received, bythe UE, from a 2G/3G network. A UE receives an LTE frequency bandinformation sent by a 2G/3G base station in the 2G/3G network. In thisway, when a return to an LTE is needed after a CSFB service, a suitablecell for residing may be selected, according to the equivalent PLMNlist, on the frequency band corresponding to the LTE frequencyinformation, and a PLMN corresponding to the stored identity informationof the LTE PLMN is selected in priority from the available PLMNs of thesuitable cell.

Specifically, a 2G/3G base station may select the LTE frequency bandinformation in any of the following way of implementations.

In one alternative way of implementation, a 2G/3G base station receivesa connection release message sent by a serving MSC/VLR, wherein, theconnection release message includes the identity information of the LTEPLMN registered when a UE initiates a CSFB service, i.e. the identityinformation of the LTE PLMN registered by the UE in the step 401. Then,the 2G/3G base station may select LTE frequency band informationaccording to the identity information of the LTE PLMN. It shall be notedthat, that 2G/3G base station may select the LTE frequency bandinformation according to the identity information of the LTE PLMN refersto that the 2G/3G base station may select LTE frequency band informationby taking the identity information of the LTE PLMN as one factor toconsider, and the 2G/3G base station may also select the LTE frequencyinformation by considering other factors, which is not limited in thisembodiment.

In another alternative way of implementation, a serving MSC/VLR does notneed to send identity information of the LTE PLMN registered by the UEto a 2G/3G base station. That is to say, each of the 2G/3G base station,the serving MSC/VLR and the like, which is in a network side adopts theexisting connection release flow. At this moment, the 2G/3G base stationmay select, according to a CSFB indication received from the servingMSC/VLR, an LTE frequency band (Frequency) information. The selected LTEfrequency band information may instruct an LTE frequency band whichprovides a CSFB service for a UE and which is supported by the servingPLMN, and it may also instruct other LTE frequency band.

Furthermore, a 2G/3G base station may send selected LTE frequency bandinformation to a UE in any of the following ways of implementation.

In one alternative way of implementation, a 2G/3G base station may sendselected LTE frequency band information to a UE by making it be includedin a connection release message or a channel release message.Specifically, if the 2G/3G base station is a BSS in a 2G network, theselected LTE frequency band information is sent to a UE by making it beincluded in the channel release message; and if the 2G/3G base stationis a RNS in a 3G network, the selected LTE frequency information is sentto a UE by making it be included in a RRC connection release message.When a connection release message or a channel release message isreceived, a UE enters into an idle state.

In another alternative way of implementation, a 2G/3G base station maymake selected LTE frequency band information be included in priorityinformation. Then, if the 2G/3G base station is a BSS in a 2G network,the 2G/3G base station sends the priority information to the UE bymaking it be included in a channel release message; and if a 2G/3G basestation is a RNS in the 3G network, the 2G/3G base station sends thepriority information to the UE by making it be included in a mobilityinformation message.

The method for selecting an LTE network, which is provided by theembodiment of the present application, comprising a UE adding identityinformation of an LTE PLMN registered when a CSFB service is initiatedto an equivalent PLMN list, and selecting, according to an updatedequivalent PLMN list, the LTE PLMN to return to the LTE network when theCSFB service ends, can ensure that the UE returns to the LTE PLMNregistered when the CSFB is initiated, which not only reduces anunnecessary inter-PLMN switch, but also recovers a data servicesuspended in the previously registered LTE PLMN, thereby improving theservice efficiency and promoting the user experience.

Another method for selecting an LTE network is provided in an embodimentof the present application, in which a UE does not need to update anequivalent PLMN list. As shown in FIG. 5, the method comprises thefollowing steps.

501, a UE performs a combined registration in an LTE PLMN.

The UE is simultaneously registered to a 2G/3G network and an LTEnetwork. A data service may be performed in the LTE network. When a CSdomain service needs to be performed, a CSFB flow may be initiated tofall back to the 2G/3G network.

502, the UE initiates a CSFB service to fall back to a 2G/3G network,and stores LTE frequency band information, wherein the LTE frequencyband information is LTE frequency band information selected when the UEinitiates a combined registration to the LTE PLMN.

Further, the UE may store identity information of the LTE PLMNregistered when the CSFB service is initiated, wherein, the storedidentity information of the LTE PLMN may be a registered LTE PLMNidentity (ID), a Tracking Area Identity (TAI) including a registered LTEPLMN ID or a Globally Unique Temporary Identity (GUTI) including aregistered LTE PLMN ID.

503, when the CSFB service ends, the UE performs a PLMN selection on afrequency band corresponding to the LTE frequency band information.

The performing a PLMN selection on a frequency band includes: selectinga suitable cell for residing on a frequency band corresponding to theLTE frequency information, and selecting an LTE PLMN in prioritycorresponding to the stored identity information of the LTE PLMN fromavailable PLMNs of the suitable cell.

The method for selecting an LTE network, which is provided in theembodiment of the present application, comprising the UE performing anPLMN selection on an LTE frequency band information selected when acombined registration is initiated, can ensure that the UE returns tothe LTE PLMN registered when the CSFB is initiated, which not onlyreduces an unnecessary inter-PLMN switch, but also recovers a dataservice suspended in the previously registered LTE PLMN, therebyimproving the service efficiency and promoting the user experience.

Another method for selecting an LTE network is provided in an embodimentof the present application. As shown in FIG. 6, the method comprises thefollowing steps.

601, a 2G/3G base station receives a connection release message sent bya serving MSC/VLR, wherein, the connection release message includesidentity information of an LTE PLMN registered when a UE initiates aCSFB service, and the 2G/3G base station is a base station whichprovides a service for the CSFB service.

Wherein, the 2G/3G base station is a base station which provides aservice for a CS service of the UE, and the UE performs the CSFB servicein a serving cell of the 2G/3G base station. For example, the 2G/3G basestation may be a BSS/RNS. In this embodiment, when the CSFB servicetriggered by the UE ends, a serving MSC/VLR may send a CSFB indication,an identity of the UE and identity information of the LTE PLMNregistered when the UE initiates the CSFB to the 2G/3G base station. Inthis way, when the CSFB service of the UE ends, an LTE networkregistered when the CSFB is initiated previously may be returned to.

It shall be noted that, if the serving MSC/VLR is a registered MSC/VLRof the UE, the serving MSC/VLR acquires the identity of the UE and theidentity information of the LTE PLMN registered by the UE fromregistration information of the UE. If the serving MSC/VLR is not aregistered MSC/VLR of the UE, the serving MSC/VLR acquires the identityof the UE and the identity information of the LTE PLMN registered by theUE from the registered MSC/VLR of the UE.

Wherein, an identity of the UE may be a System Architecture Evolution(SAE) Temporary Mobile Subscriber Identity (S-TMSI), an InternationalMobile Subscriber Identity (IMSI) or Temporary Mobile SubscriberIdentity (TMSI), which is not limited in an embodiment of the presentapplication. Identity information of the LTE PLMN registered when the UEinitiates the CSFB service may be a registered LTE PLMN identity (ID);it may also be a Globally Unique Temporary Identity (GUTI) including aregistered LTE PLMN ID; it may also be a Tracking Area Identity (TAI)including registered LTE PLMN ID; and it may also be an E-UTRAN CellGlobal Identity (ECGI) including a registered LTE PLMN ID, which is notlimited in an embodiment of the present application.

602, the 2G/3G base station selects, according to the identityinformation of the LTE PLMN, target frequency band information and sendsthe target frequency band information to the UE. The target frequencyband information is used for indicating the UE to select a cell on afrequency band corresponding to the target frequency band informationfor residing.

The 2G/3G base station selects, according to the identity information ofthe LTE PLMN, target frequency band information, refers to that the2G/3G base station may select the LTE frequency band information bytaking the identity information of the LTE PLMN as a factor to consider,and may also select the LTE frequency information by considering otherfactors, which is not limited in this embodiment.

Further, the sending the target frequency information to the UEincludes: the 2G/3G base station may specifically transmit the selectedtarget frequency band information to the UE in any of the following waysof implementation.

In one alternative way of implementation, a 2G/3G base station may sendselected target frequency band information to a UE by making it beincluded in a connection release message or a channel release message.Specifically, if a 2G/3G base station is a BSS in a 2G network, theselected target frequency information is sent to a UE by making it beincluded in a Channel Release message; and if a 2G/3G base station is aRNS in a 3G network, the selected target frequency information is sentto a UE by making it be included in an RRC connection release message.When a UE receives a connection release message or a Channel Releasemessage, the UE enters into an idle state.

In another alternative way of implementation, a 2G/3G base station maymake selected target frequency band information be included in priorityinformation. Then, if the 2G/3G base station is a BSS in a 2G network,the 2G/3G base station sends the priority information to the UE bymaking it be included in the channel release message; and if a 2G/3Gbase station is a RNS in a 3G network, the 2G/3G base station sendspriority information to a UE by making it be included in mobilityinformation.

For the UE, the UE selects, according to an equivalent PLMN list, asuitable cell for residing on an LTE frequency band corresponding totarget frequency information selected by a 2G/3G base station, andselects a PLMN in priority corresponding to identity information of anLTE PLMN from available PLMNs of the suitable cell. It shall be notedthat, in this way of implementation, if a UE has already stored LTEfrequency band (Frequency) information selected when a combinedregistration is initiated in an LTE PLMN, the UE may in priority select,according to the stored equivalent PLMN list, a suitable cell forresiding on an LTE frequency band corresponding to the stored LTEfrequency band information, and in priority selects a PLMN correspondingto the stored identity information of the LTE PLMN from the availablePLMNs of the suitable cell.

The method for selecting an LTE network, which is provided by theembodiment of the present application, comprising when a CSFB service ofa UE ends, a 2G/3G base station selecting target frequency bandinformation according to the identity information of an LTE PLMNregistered by a UE and sending it to the UE, so that when a connectionestablishment request to an LTE network is initiated, the UE selects anLTE cell to reside on a frequency band corresponding to the targetfrequency information, can ensure that the UE returns to the LTE PLMNregistered when the CSFB is initiated, which not only reduces anunnecessary inter-PLMN switch, but also recovers a data servicesuspended in the previously registered LTE PLMN, thereby improving theservice efficiency and promoting the user experience.

A UE is provided in another embodiment of the present application. Asshown in FIG. 7, the UE comprises: a processor 72 and a receiver 71.

The receiver 71 is used for receiving an equivalent PLMN list from a2G/3G network when the UE performs a combined registration in an LTEPLMN and initiating a CSFB service and falls back to the 2G/3G network.

The processor 72 is used for adding identity information of the LTE PLMNto the equivalent PLMN list received by the receiver 71, and performing,according to the equivalent PLMN list, a PLMN selection when the CSFBservice ends.

Furthermore, the processor 72 is used for selecting the LTE PLMN inpriority according to the equivalent PLMN list.

Alternatively, the processor 72 is used for selecting, according to theequivalent PLMN list, a cell on a frequency band corresponding to LTEfrequency band information, and selecting the LTE PLMN in priority fromavailable PLMNs for the cell, wherein, the LTE frequency bandinformation is information of an LTE frequency band selected when the UEinitiates a combined registration to the LTE PLMN.

Alternatively, the processor 72 is used for selecting, according to theequivalent PLMN list, a cell on a frequency band corresponding to LTEfrequency band information, and selecting the LTE PLMN in priority fromavailable PLMNs for the cell, wherein the LTE frequency band informationis received, by the UE, from the 2G/3G network.

Through adding identity information of an LTE PLMN registered when aCSFB service is initiated to an equivalent PLMN list, and selecting,according to an updated equivalent PLMN list, the LTE PLMN to return tothe LTE network when the CSFB service ends, the UE, provided in theembodiment of the present application, can ensure that the UE returns tothe LTE PLMN registered when the CSFB is initiated, which not onlyreduces an unnecessary inter-PLMN switch, but also recovers a dataservice suspended in the previously registered LTE PLMN, therebyimproving the service efficiency and promoting the user experience.

A UE is provided in another embodiment of the present application. Asshown in FIG. 8, the UE comprises: a transceiver 81 and a processor 82.

The transceiver 81 is used for interacting with a network device toperform a combined registration in an LTE PLMN.

The processor 82 is used for performing a PLMN selection on a frequencyband corresponding to LTE frequency band information when a CSFB serviceends, wherein, the LTE frequency band information is information of anLTE frequency band selected when the UE initiates a combinedregistration to the LTE PLMN.

Furthermore, the processor 82 is used for selecting a cell on thefrequency band corresponding to the LTE frequency band information, andselecting the LTE PLMN in priority from available PLMNs for the cell.

Furthermore, the UE further comprises a storage 83.

The storage 83 is used for storing the LTE frequency band informationwhen the transmitter initiates the CSFB service to fall back to acircuit domain.

The processor 82 is also used for acquiring the LTE frequency bandinformation from the storage when the CSFB service ends.

Through performing an PLMN selection on an LTE frequency bandinformation selected when a combined registration is initiated, the UE,provided in the embodiment of the present application, can ensure thatthe UE returns to the LTE PLMN registered when the CSFB is initiated,which not only reduces an unnecessary inter-PLMN switch, but alsorecovers a data service suspended in the previously registered LTE PLMN,thereby improving the service efficiency and promoting the userexperience.

A 2G/3G base station is provided, which is used for providing servicefor a CSFB service. As shown in FIG. 9, the 2G/3G base station comprisesa receiver 91, a processor 92 and a transmitter 93.

The receiver 91 is used for receiving a connection release message sentby a serving MSC/VLR, wherein, the connection release message comprisesidentity information of an LTE PLMN registered when a UE initiates aCSFB service.

The processor 92 is used for selecting, according to the identityinformation of the LTE PLMN which is received by the receiver 91, targetfrequency band information, wherein, the target frequency bandinformation is used for indicating the UE to select a cell for residingon a frequency band corresponding to the target frequency bandinformation;

The transmitter 93 is used for sending the target frequency bandinformation selected by the processor 92 to the UE.

Furthermore, the transmitter 93 is used for sending priority informationto the UE, wherein, the priority information comprises the frequencyband information.

Through selecting target frequency band information according to theidentity information of an LTE PLMN registered by a UE and sending it tothe UE, so that when a connection establishment request to an LTEnetwork is initiated, the UE selects an LTE cell to reside on afrequency band corresponding to the target frequency information, the2G/3G base station, provided in the embodiment of the presentapplication, can ensure that the UE returns to the LTE PLMN registeredwhen the CSFB is initiated, which not only reduces an unnecessaryinter-PLMN switch, but also recovers a data service suspended in thepreviously registered LTE PLMN, thereby improving the service efficiencyand promoting the user experience.

An LTE base station is provided in another embodiment of the presentapplication. As shown in FIG. 10, the base station comprises a receiver1001 and a processor 1002.

The receiver 1001 is used for receiving a connection establishmentrequest message sent by a UE when a CSFB service ends, wherein, theconnection establishment request message comprises an identity of theUE.

The processor 1002 is used for selecting, according to the identity ofthe UE and identity information of the LTE PLMN registered when the UEinitiates the CSFB service, the LTE PLMN corresponding to the identityinformation of the LTE PLMN.

Further alternatively, the LTE base station alternatively furthercomprises: a storage 1003.

The receiver 1001 is further used for receiving the identity of the UEand the identity information of the LTE PLMN, which are sent by a 2G/3Gbase station, wherein, the 2G/3G base station is a base station whichprovides service for the CSFB service.

The storage 1003 is used for storing the identity of the UE and theidentity information of the LTE PLMN, which are sent by the 2G/3G basestation and received by the receiver 1001.

Furthermore, the receiver 1001 is further used for receiving aconnection release message sent by a serving MSC/VLR, wherein, theconnection release message comprises an identity of the UE and identityinformation of the LTE PLMN, and sending the identity of the UE and theidentity information of the LTE PLMN to the LTE base station.

Furthermore, when the serving MSC/VLR is a registered MSC/VLR of the UE,the identity of the UE and the identity information of the LTE PLMN isacquired from a registration information of the UE by the servingMSC/VLR; or,

when the serving MSC/VLR is not a registered MSC/VLR of the UE, theidentity of the UE and the identity information of the LTE PLMN isacquired from the registered MSC/VLR by the serving MSC/VLR.

Further alternatively, the LTE base station is alternatively a basestation which provides access service when the UE initiates the CSFBservice; and the LTE base station further comprises: a storage 1003,used for storing the identity of the UE and the identity information ofthe LTE PLMN when the UE initiates the CSFB service in the LTE PLMN.

Furthermore, the processor 1002 is further used for deleting the storedidentity of the UE and the identity information of the LTE PLMN.

Through determining and selecting the identity information of the LTEPLMN by matching the identity of the UE sent by the UE with the storedidentity of the UE, the LTE base station, which is provided in theembodiment of the present application, can ensure that the UE returns tothe LTE PLMN registered when the CSFB is initiated, which not onlyreduces an unnecessary inter-PLMN network switch, but also recovers adata service suspended in the previously registered LTE PLMN, therebyimproving the service efficiency and promoting the user experience,compared with the method, defined in the prior art, which returns to anLTE network after a CSFB.

A UE is provided by another embodiment of the present application. Asshown in FIG. 11, the UE comprises:

a registering unit 1101, used for performing a combined registration inan LTE PLMN;

a fallback unit 1102, used for initiating a CSFB service to fall back toa 2G/3G network;

a receiving unit 1103, used for receiving an equivalent PLMN list in the2G/3G network;

an adding unit 1104, used for adding identity information of the LTEPLMN to the equivalent PLMN list received by the receiving unit 1103;and

a selecting unit 1105, used for performing, according to the equivalentPLMN list modified by the adding unit 1104, a PLMN selection when theCSFB service ends.

Furthermore, the selecting unit 1105 is used for selecting, according tothe equivalent PLMN list modified by the adding unit 1104, the LTE PLMNin priority.

Further alternatively, the selecting unit 1105 is specifically used forselecting, according to the equivalent PLMN list modified by the addingunit 1104, a cell on a frequency band corresponding to LTE frequencyband information; and selecting the LTE PLMN in priority from availablePLMNs for the cell;

wherein, the LTE frequency band information is information of an LTEfrequency band selected when the UE initiates a combined registration tothe LTE PLMN.

Further alternatively, the selecting unit 1105 is specifically used for:

selecting, according to the equivalent PLMN list modified by the addingunit 1104, a cell on a frequency band corresponding to LTE frequencyband information; and selecting the LTE PLMN in priority from availablePLMNs for the cell;

wherein, the LTE frequency band information is received from the 2G/3Gnetwork by the UE.

Through adding identity information of an LTE PLMN registered when aCSFB service is initiated to an equivalent PLMN list, and selecting,according to an updated equivalent PLMN list, the LTE PLMN to return tothe LTE network when the CSFB service ends, the UE, which is provided bythe embodiment of the present application, can ensure that the UEreturns to the LTE PLMN registered when the CSFB is initiated, which notonly reduces an unnecessary inter-PLMN network switch, but also recoversa data service suspended in the previously registered LTE PLMN, therebyimproving the service efficiency and promoting the user experience.

A UE is provided in another embodiment of the present application. Asshown in FIG. 12, the UE comprises a registering unit 1201 and aselecting unit 1202.

The registering unit 1201, used for performing a combined registrationin an LTE PLMN;

The selecting unit 1202, used for performing a PLMN selection on afrequency band corresponding to LTE frequency band information when aCSFB service ends, wherein, the LTE frequency band information isinformation of an LTE frequency band selected when the UE initiates acombined registration to the LTE PLMN.

Furthermore, the selecting unit 1202 is used for:

selecting a cell on the frequency corresponding to the LTE frequencyinformation, and selecting the LTE PLMN in priority from available PLMNsfor the cell.

Furthermore, the UE further comprises a storing unit 1203.

The storing unit 1203, used for storing the LTE frequency bandinformation when the CSFB service is initiated the and a CS domain isfallen back to.

The selecting unit 1202 is further used for acquiring the LTE frequencyinformation from the storing unit when the CSFB service ends.

Through performing a PLMN selection on the selected LTE frequency bandinformation when a combined registration is initiated, the UE, which isprovided in the embodiment of the present application, can ensure thatthe UE returns to the LTE PLMN registered when the CSFB is initiated,which not only reduces an unnecessary inter-PLMN network switch, butalso recovers a data service suspended in the previously registered LTEPLMN, thereby improving the service efficiency and promoting the userexperience.

A 2G/3G base station is provided in the embodiment of the presentapplication, which is used for providing service for a CSFB service. Asshown in FIG. 13, the base station comprises a receiving unit 1301, aselecting unit 1302 and a sending unit 1303.

The receiving unit 1301, used for receiving a connection release messagesent by a serving MSC/VLR, wherein, the connection release messagecomprises identity information of an LTE PLMN registered when a UEinitiates a CSFB service.

The selecting unit 1302 is used for selecting, according to the identityinformation of the LTE PLMN which is received by the receiving unit1301, target frequency band information, wherein, the target frequencyband information is used for indicating the UE to select a cell forresiding on a frequency band corresponding to the target frequency bandinformation.

The sending unit 1303 is used for sending the target frequency bandinformation selected by the selecting unit 1302 to the UE.

Furthermore, the sending unit 1303 is used for:

sending priority information to the UE, wherein, the priorityinformation comprises the frequency band information.

Through selecting target frequency band information according to theidentity information of an LTE PLMN registered by UE and sending it tothe UE, so that when a connection establishment request to an LTEnetwork is initiated, the UE selects an LTE cell to reside on afrequency band corresponding to the target frequency information, thebase station, which is provided by the embodiment of the presentapplication, can ensure that the UE returns to the LTE PLMN registeredwhen the CSFB is initiated, which not only reduces an unnecessaryinter-PLMN network switch, but also recovers a data service suspended inthe previously registered LTE PLMN, thereby improving the serviceefficiency and promoting the user experience.

A base station is provided in another embodiment of the presetapplication, and the base station may be an LTE base station. As shownin FIG. 14, the base station comprises a receiving unit 1401 and aselecting unit 1402.

The receiving unit 1401, used for receiving a connection establishmentrequest message sent by a UE when a CSFB service ends, wherein, theconnection establishment request message comprises an identity of theUE.

The selecting unit 1402, used for selecting, according to the identityof the UE and identity information of LTE PLMN registered when the UEinitiates the CSFB service, which are received by the receiving unit1401, the LTE PLMN corresponding to the identity information of the LTEPLMN.

Furthermore, the receiving unit 1401 is further used for:

before receiving the identity of the UE and the identity information ofthe LTE PLMN sent by a 2G/3G base station, receiving, by the 2G/3G basestation, a connection release message sent a serving MSC/VLR, wherein,the connection release message comprises the identity of the UE and theidentity information of the LTE PLMN and the 2G/3G base station sendsthe identity of the UE and the identity information of the LTE PLMN tothe 2G/3G base station.

Furthermore, when the serving MSC/VLR is a registered MSC/VLR of the UE,the identity of the UE and the identity information of the LTE PLMN isacquired from a registration information of the UE by the servingMSC/VLR; or,

when the serving MSC/VLR is not a registered MSC/VLR of the UE, theidentity of the UE and the identity information of the LTE PLMN isacquired from the registered MSC/VLR by the serving MSC/VLR.

Furthermore, the base station is a base station which provides an accessservice when the UE initiates the CSFB service; and the LTE base stationfurther comprises:

a storing unit 1403, used for saving the identity of the UE and theidentity information of the LTE PLMN when the UE initiates the CSFBservice in the LTE PLMN.

Furthermore, the base station further comprises a deleting unit 1404.

The deleting unit 1404 is used for deleting the stored identity of theUE and the identity information of the LTE PLMN.

Through determining and selecting the identity information of the LTEPLMN by matching the identity of the UE sent by the UE with the storedidentity of the UE, the base station, which is provided in theembodiment of the present application, can ensure that the UE returns tothe LTE PLMN registered when the CSFB is initiated, which not onlyreduces an unnecessary inter-PLMN network switch, but also recovers adata service suspended in the previously registered LTE PLMN, therebyimproving the service efficiency and promoting the user experience,compared with the method of returning to an LTE network after a CSFBwhich is defined by the prior art.

Through the description of the embodiments above, those skilled in theart to which the present application pertains may clearly understandthat, the present application can be realized through software withnecessary general hardware, or certainly, it may also be realizedthrough hardware, but in most cases, the former is a better way ofimplementation. Based on this kind of understanding, the technicalsolution of the present application or the contribution part of thepresent application to the prior art can be embodied substantially inthe form of a software product. The computer software product is storedin a readable storage medium, such as a soft disk, a hard disk, anoptical disk or the like of a computer, which includes a plurality ofinstructions enabling computer device (it may be a personal computer, aserver, a network device or the like) to execute the methods of theembodiments of the present application.

What described above are merely some specific embodiments of the presentapplication, however, the protection scope of the present application isnot to limit to them. Any change or substitution that is readilyconceived for any one skilled in the art within the technical scopedisclosed by the application shall fall into the protection scope of theapplication. Therefore, the protection scope of the present applicationshall be defined by the claims.

What is claimed is:
 1. A method for selecting a Long Term Evolution(LTE) network, comprising: receiving, by a 2nd generation/3rd generation(2G/3G) base station, a connection release message sent by a servingMobile Switching Centre/Visitors Location Register (MSC/VLR), wherein,the connection release message comprises identity information of an LTEPublic Land Mobile Network (PLMN) registered when a user equipment UEinitiates a CSFB service, and the 2G/3G base station is a base stationwhich provides a service for the CSFB service; selecting, by the 2G/3Gbase station, target frequency band information according to theidentity information of the LTE PLMN; and sending the target frequencyband information to the UE, wherein, the target frequency bandinformation is used for indicating the UE to select a cell for residingon a frequency band corresponding to the target frequency bandinformation.
 2. The method according to claim 1, wherein the sending thetarget frequency band information to the UE comprises: sending priorityinformation to the UE, wherein, the priority information comprises thefrequency band information.
 3. A method for selecting a Long TermEvolution (LTE) network, comprising: receiving, by an LTE base station,a connection establishment request message sent by a UE when a CircuitSwitched Fallback (CSFB) service ends, wherein, the connectionestablishment request message comprises an identity of the UE; andselecting, by the LTE base station, in accordance with the identity ofthe UE and identity information of an LTE Public Land Mobile Network(PLMN) registered when the UE initiates the CSFB service, the LTE PLMNcorresponding to the identity information of the LTE PLMN.
 4. The methodaccording to claim 3, wherein the method further comprises: receivingand storing, by the LTE base station, the identity of the UE and theidentity information of the LTE PLMN, which are sent by a 2ndgeneration/3rd generation (2G/3G) base station, wherein, the 2G/3G basestation is a base station which provides service for the CSFB service.5. The method according to claim 4, wherein before receiving, by the LTEbase station, the identity of the UE and the identity information of theLTE PLMN, which are sent by the 2G/3G base station, the method furthercomprises: receiving, by the 2G/3G base station, a connection releasemessage sent by a serving Mobile Switching Centre/Visitors LocationRegister (MSC/VLR), wherein, the connection release message comprisesthe identity of the UE and the identity information of the LTE PLMN;sending, by the 2G/3G base station, the identity of the UE and theidentity information of the LTE PLMN to the LTE base station.
 6. Themethod according to claim 5, wherein if the serving MSC/VLR is aregistered MSC/VLR of the UE, the identity of the UE and the identityinformation of the LTE PLMN are acquired, by the serving MSC/VLR, fromregistration information of the UE.
 7. The method according to claim 5,wherein if the serving MSC/VLR is not a registered MSC/VLR of the UE,the identity of the UE and the identity information of the LTE PLMN areacquired, by the serving MSC/VLR, from the registered MSC/VLR of the UE.8. The method according to claim 3, wherein the LTE base station is abase station which provides an access service when the UE initiates theCSFB service, and the method further comprises: storing, by the LTE basestation, the identity of the UE and the identity information of the LTEPLMN when the UE initiates the CSFB service in the LTE PLMN.
 9. Themethod according to claim 4, wherein the method further comprises:deleting, by the LTE base station, the stored identity of the UE and theidentity information of the LTE PLMN.
 10. A 2nd generation/3rdgeneration (2G/3G) base station, providing service for a CircuitSwitched Fallback (CSFB) service, comprising: a receiver device,configured to receive a connection release message sent by a servingMobile Switching Centre/Visitors Location Register (MSC/VLR), wherein,the connection release message comprises identity information of an LTEPublic Land Mobile Network (PLMN) registered when a user equipment UEinitiates a CSFB service; a processor device, configured to select,according to the identity information of the LTE PLMN which is receivedby the receiver device, target frequency band information, wherein, thetarget frequency band information is used for indicating the UE toselect a cell for residing on a frequency band corresponding to thetarget frequency band information; a transmitter device, configured tosend the target frequency band information selected by the processordevice to the UE.
 11. The 2G/3G base station according to claim 10,wherein the transmitter device is configured to: send priorityinformation to the UE, wherein, the priority information comprises thefrequency band information.
 12. A Long Term Evolution (LTE) basestation, comprising: a receiver device, configured to receive aconnection establishment request message sent by a user equipment (UE)when a Circuit Switched Fallback (CSFB) service ends, wherein, theconnection establishment request message comprises an identity of theUE; and a processor device, configured to select, according to theidentity of the UE and identity information of the LTE Public LandMobile Network (PLMN) registered when the UE initiates the CSFB service,the LTE PLMN corresponding to the identity information of the LTE PLMN.13. The LTE base station according to claim 12, further comprising: astorage device, wherein the receiver device is further configured toreceive the identity of the UE and the identity information of the LTEPLMN, which are sent by a 2nd generation/3rd generation (2G/3G) basestation, wherein, the 2G/3G base station is a base station whichprovides service for the CSFB service; and the storage device isconfigured to store the identity of the UE and the identity informationof the LTE PLMN, which are sent by the 2G/3G base station and receivedby the receiver device.
 14. The LTE base station according to claim 12,wherein the LTE base station is a base station which provides accessservice when the UE initiates the CSFB service; and the LTE base stationfurther comprises: a storage device, configured to store the identity ofthe UE and the identity information of the LTE PLMN when the UEinitiates the CSFB service in the LTE PLMN.
 15. The LTE base stationaccording to claim 13, wherein the processor device is furtherconfigured to delete the stored identity of the UE and the identityinformation of the LTE PLMN.